In the NTSC color TV system, the composite video signal consists of luminance and chrominance components and harmonics which are frequency-interleaved in order to minimize interference therebetween, e.g. beat, crosstalk, etc. Thus, the subcarrier encoded by the chrominance component is put on a region of the frequency spectrum which is free from signal energy of the luminance component. A comb filter may be used to separate the luminance and chrominance components from the composite video signal. The comb filter has a filter characteristic shaped like a comb, with the spacing between the teeth equal to the horizontal scanning frequency of the TV signal. The comb filter improves horizontal resolution in the region about 3.58 MHz and cross color in comparison with conventional bandpass and bandreject filters.
A conventional comb filter is shown in FIG.1, and comprises a delay line 10, and two summing devices 12 and 14. The delay line 10 delays the input video signal for one line duration, about 63.56 .mu.s. The comb filtered chrominance component is derived from an output terminal A by subtracting the input video signal from the delayed video signal and the comb filtered luminance component is derived from an output terminal B by summing the input and the delayed video signals. A detailed description of the operation of the conventional comb filter is not provided, because it is well known. In the illustrated conventional comb filter, the comb filtered luminance component and the comb filtered chrominance component have distinct signal paths even though the output of the delay line 10 is used to generate both components.